In this study, we present an analytical model for modelling two-phase flow of silica sol grouting in a single rock fracture. This model considers the time-dependent rheological property of the silica sol. The impact of groundwater flow in silica sol grouting is investigated by comparing the results of the present two-phase flow model with that of the single-phase flow model ignoring the groundwater flow. It generally shows that the groundwater flow significantly affects the pressure distribution and grouts penetration in the fracture. Ignoring the groundwater flow in single-phase flow models will underestimate the pressure at the propagation front and overestimate the propagation length. The analytical model presented in this study is able to describe the more realistic two-phase processes in rock grouting, which can be readily used in practice to reduce the potential uncertainties in the application of previous simplified analytical models.